The present invention relates to laser drilling systems, and more particularly, to a method for aligning a workpiece in a laser drilling system.
Material ablation by pulsed light sources has been studied since the invention of the laser. Reports in 1982 of polymers having been etched by ultraviolet (UV) excimer laser radiation stimulated widespread investigations of the process for micromachining. Since then, scientific and industrial research in this field has proliferatedxe2x80x94mostly spurred by the remarkably small features that can be drilled, milled, and replicated through the use of lasers.
Ultrafast lasers generate intense laser pulses with durations from roughly 10xe2x88x9211 seconds (10 picoseconds) to 10xe2x88x9214 seconds (10 femtoseconds). Short pulse lasers generate intense laser pulses with durations from roughly 10xe2x88x9210 seconds (100 picoseconds) to 10xe2x88x9211 seconds (10 picoseconds). A wide variety of potential applications for ultrafast and short pulse lasers in medicine, chemistry, and communications are being developed and implemented. These lasers are also a useful tool for milling or drilling holes in a wide range of materials. Hole sizes as small as a few microns, even sub-microns, can readily be drilled. High aspect ratio holes can be drilled in hard materials, such as cooling channels in turbine blades, nozzles in ink-jet printers, or via holes in printed circuit boards.
Optical parallel processing of laser-milled holes is key to increasing the throughput of, and the profitability of laser micromachining. Beam splitting devices such as diffractive optical elements (DOE) are currently used in laser micromachining to divide a single beam into multiple beams to allow for parallel processing of the workpiece (material to be drilled). The multiple sub-beams are focused at a focal plane that is a specific distance from the final lens in a laser drilling system. The focal plane is a plane located at a distance f, which is equal to the focal length of the lens and normal to the optical axis of the beam delivery system.
The target area is comprised of the area of the workpiece where the hole pattern is drilled. The entire target area of the workpiece must be positioned in the focal plane of the sub-beams to ensure consistency of size and shape across all holes being drilled. If the entire target area is not in the focal plane, some of the beams drilling the holes in workpiece will be out of focus when they reach the workpiece, thereby causing the drilled holes not to meet size and shape requirements. What is needed is a way to keep the target area of the workpiece in the focal plane of the laser beam in a laser drilling system.
In accordance with the present invention, a method is provided for aligning a workpiece in a laser drilling system. The method includes: providing a workpiece having at least two substantially planar and parallel surfaces, including a first planar surface in which ablations are formed therein by the laser drilling system; propagating an alignment beam of light towards a second planar surface of the workpiece, the alignment beam being incident on and reflected by the second planar surface, thereby forming a reflected beam of light; measuring a reflection angle of the reflected beam; and determining alignment information for the workpiece based on the measured reflection angle of the reflected beam. The method may further include adjusting alignment of the workpiece based on the alignment information.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.